Pulse forming and shaping circuits



Dec. 4, 1951 4 Sheets-Sheet 1 Filed Dec. 9, 1944 PULSE UTILIZATION c/ncurr was: man/Iva A/VDSHAPING CIRCUIT RECEIVER TRANSMITTER 7 Y Y 1 i Y 4 9/ 5 2 6 m 3 3 Z) 7 Y Y V, 3 2 W w G v w. 5 u 4 3 F W) w m K m m ag M K w x 1 4 m g m 6 Y Y 5E8! F X X w uzimiu 9 5 x 2 0 Y M m T I 3 a w w 5 r L. m 5 P W 5 v .1 u M a P w w m M x 1 x INVENTOR BM OLIVER BY ATTORNEY Dec. 4, 1951 B. M. OLIVER 2,577,355

PULSE FORMING AND SHAPING CIRCUITS Filed Dec. 9, 1944 4 Sheets-Sheet 2 FIG. .5

VOLTAGE INPUT 7D VI VOLUME CURRENT ourpur 0F CLIPPER TUBE w CURRE N T VOLTAGE INPUT T0 TUBE V3 VOLTAGE OUTPUT or V:

cur-arr Bus /54 or AMPLIFIER as VOL TAGE AMPLIFIED VOL 74c: ourpu I TIME BM. OLIVER BY A T TORNE V Dec. 4, 1951 B. M. OLIVER PULSE FORMING AND SHAPING CIRCUITS 4 Sheets-Sheet 5 Filed Dec. 9, 1944 FIG. 6 VOLTAGE INPUT T0 VI 4 m w N m Tw T M F w 0 W s R A T m NM r P F RI 0 u w C 0 v 3 U 2 m W B v01. mas INPUT cur- OFF BIAS /92 057095 v:

OF v:

OUTPUT OF CLIPPER 50 AMPLIFIED VOL TA GE OUTPUT TIME NuvR QQA '44 l ATTORNKY B. M. OLIVER PULSE FORMING AND SHAPING CIRCUITS Filed- Dec. 9, 1944 VOL T465 VOL TAGE CURREIV T FIG. 7

VOLTAGE INPUT T0 VI CUT-OFF BIAS 0F TUBE VI Sheets-Sheet 4 CLIPPER TUBE VI I33 [tanks/v1 OUTPUT 0F vaLmaz nvPur TIME AMPLIFIED Eur-arr, or was v.1

VOLUME-OUTPUT or v.1

VOL TAGE OUTPUT INVENTOP B. M OLIVER BY ATTORNEY Patented Dec. 4, 1951 PULSE FORMING AND SHAPING CIRCUITS Bernard M. Oliver, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 9, 1944, Serial No. 567,406

3 Claims. (Cl. 25027) This invention relates to electric circuits and 7 more specifically to pulse forming and shaping circuits. e

In a pulse reflection type image locating and distance measuring system (frequently called a, radar) ultra-high frequency waves are directively emitted in pulses of veryshort time duration; reflections thereof are received from objects upon which the emitted pulses impinge; and the reflection delay times for particular objects are determined to provide indications of the distances to the objects from which the respective reflected signals are received. Electrical variations received at the receiving point constitute a plurality of impulses, which might be made up, for example, of a series of trains of pulses, each train comprising, for example, a transmitted. pulse and one or more reflections or echo pulses from objects in the radio beam interspersed with and supplemented by variations due to noise, etc. Due to difierences in size and distance of the objects from which pulses are reflected and to many other causes, including the depth of the object, the echo pulses are not of the same size and shape and some are of much longer duration, than others. Frequently the need arises, such as in radar equipment normally making use of echo' pulses for tracking or other purposes, for apparatus for producing a series of impulses of substantially equal intensity and duration from the. series of impulses in the output of the receiver. The present invention, in one of its aspects, serves to answer this need. In another of its aspects, the invention relates to the provision of a circuit arrangement for producing a group or series of. rectangularly shaped pulses, all of the same amplitude, from a group or series of pulses, at least some of which are dissimilar in shape or width and which may be of dissimilar amplitude. In one of its aspects the present invention is directed to means for forming a train of pulses of substantially uniform shape and size from a train of pulses some at least of which are dissimilar in shape or size.

In accordance with a'somewhat different aspect of the invention, there is provided apparatus for forming trains or series of rectangularly shaped pulses from a plurality of pulses some at least of which are non-rectangular in shape.

The invention may also be broadly characterized as novel means for transforming pulses into other pulses so as to control the character of the latter.

In accordance with one illustrative embodiment of theinvention, there is provided a pulse forming and shaping circuit adapted to have applied thereto a. plurality of trains of signal pulses, the various pulses of each train in general having dissimilar shapes, amplitudes and spacings from adjacent pulses, but the amplitude, shape and spacing of each pulse in the train being substantially equivalent to that of the corresponding pulse in the immediately preceding and following series, and to produceinits output circuit a series of square-topped pulses of substantially constant amplitude and similar shape, the starting time of each of the output pulses coinciding with the starting time of each of the pulses in the corresponding input series. The incoming signals to the pulse forming and shaping circuit are amplified and inverted in polarity if necessary to produce the positive pulses. The positive pulses are then applied to a clipper tube which removes all the noise variations below a certain level from the series of pulses. The output of this tube is applied to a shaping network comprising an inductance member and a capacity member connected in a series circuit including a source of potential, the inductance member being shunted by means for damping out certain of the oscillations produced in the circuit. In this particular embodiment, the damping means comprises the grid-cathode circuit of a following amplifier tube. The tuned circuit comprising the condenser and the inductance member isv shock-excited by the pulses from the clipper tube and each of the resultant oscillations is damped within a fraction of an oscillation cycle. The duration of the output pulse can be changed by varying the constants of the tuned circuit.- This duration is less than the duration of the pulses in the output of the clipper. The tuned circuit causes shaping of the pulses by generating a cosinusoidal oscillation in response to the leading edge of each pulse, the first quarter cycle (negative) of this oscillation being used, the remainder of this oscillation, as well as the entire oscillation which would normally have been set up in response to the trailing edge, being damped by the damping means. Both the upper and lower portions of the pulses produced by the tuned circuit are clipped and the intermediate portion amplified to produce square-topped pulses of constant amplitude and of constant duration. 5

In a second illustrative embodiment, the tuned shaping network comprises an inductance member and a condenser member connected in a series circuit as in the first embodiment but damping is provided by means of a diode con nected across the inductance member in such a Way that its anode is grounded. In this arrangement, the oscillation which normally would be set up in the tuned circuit by the leading edge of each of the pulses is immediately damped and only the first quarter cycle (positive) of the oscillation initiated by the trailing edge of each pulse is utilized, the remainder of thisoscillation being damped. The clipping amplifiertube immediately following the tuned circuit is biased to cut-off in this embodiment, while in the preceding embodiment this corresponding tube-is normally conducting in the absence of pulse signals in its input circuit.

In a third illustrative enibodimentgthe-tuned shaping network comprises a parallel-connected inductance member and a condensermember. .In

such an arrangement, the oscillation initiated in the shaping network intercepts the zero "axis-at a point where the time t=T/4+At/2 where 'T!=21r/w=the :period of the oscillation, .and JM is the widthof the driving ;pulse,.t ibeingztaken equal to zero at the start of the'iinputpulse :(the -pulse used toshock-excite the tunedcircuit). :At this point the oscillation becomes :positive Land-is =damped by damping mean similar 'tQth'at' in the first embodiment. "The p-ulsesr'areclipped at both lower and upperends and the intermediate portionamplifiedasbefore.

The invention will be more readily understood by referring to the followingdescription taken in connection with'the accompanying drawings forming aparttherecf in which:

Fig. 1 is a block diagramo'f an object detecting and distance measuring system :or the pulse *reflection type;

-Fig. 2 is 'a more detailed schematic circuitdiagram of the portion- '14 -o'f the' systemsho'wnin Fig. '1;

Figs. 3 and-'4 illustratemodifications of the-por- 'tion of the circuit shown in Fig. z between lines XX and YY; and

Figs. 5, 6 and 7 are various graphical representations to aid in understanding the operation of the arrangementsof Figs. '2, 3 and 4,-respectively.

Referring more specifically to the drawings, Fig. 1-shows, by way of example to illustrate the invention =and in block diagram 'form, an object detecting and distance measuring system of the pulse reflection type. 'In the arrangement of Fig. 1, a transmitter i is provided-to suppl-yultra- "high frequency pulse-modulated radio waves (usually called-transniitted pulses or emitted pulses) which'can be directedat variou objects by meansof an antenna H. By way'o'fiexample, transmitter fl! can-comprise an oscillator for pro- "viding a sine wavehaving a suitable periodicity, "such as 400 cycles per secondjfor example. "This oscillator energizes'a'pulse generator of any one of several suitable types well known in the art;

"for example, see United States Patent 2,117,752,

mitting antenna -l l (echoes) are received by a receiving antenna :12. *The antennas ll and T2 are of :anyzsuitable i'type; for "example, they ':can

be of the polystyrene polyrod type disclosed in anapplication of G. Mueller,: Serial No 469,284,

4 filed December 17, 1942, and which issued as Pat ent 2,425,336 on August 12, 1947. The transmitted pulses and the reflection thereof picked up by the receiving antenna 12 are applied to a receiver [3 of any suitable form wherein they are, for example, amplified, detected, further amplified and applied to the pulse forming and shaping circuit I4 whichlmay comprise one .01" the circuits shown-in Figs. 2, 3 and4. The input pulse Wave to the pulse shaping circuit M is shown in Fig. 'at line A, while the output pulse wave from such a .circuitw-lflicomprises a pulse wave of the type shown in line E of Fig. 5, 6 or '7. The output waveso'f one ofthepulse shaping circuits of this invention-can .b'e:applied to an oscilloscope for directvisual' indication of the echo pulses (or ;-rather their :counterparts produced by the pulse shaping circuit I4) or they may be applied to an automatic tracking circuit arrangement of the type disclosed in a copending application of ..B. M. -O1iver,SerialiNo. 486,780, filed May 13,1943, aand whichissuedasPatent 2,433,863on January 6, 1948. Such an oscilloscope or automatic tracking arrangement Eha's been characterized as a pulse --utiliza'tion circuit and represented by the box 15. As' the'pulse utilization circuit forms no part of the present invention, it is met being described in detail.

Reference will now be made to Fig. '2 which shows in circuit diagram form one embodiment of a pulse shap'ingcircuit l4 and to Fig. 5 which shows relationships of voltage versus time and currentversus-time at' various points :in'the circuit ,oil ig. 2. 'A plurality of trains of electrical variations -'such:as that shown in-Fig. 5, line A, and repeat'ed,'for example, 400 times per second, is formed in the output circuit of the amplifier 213 of any"'well-'-known construction. Each train may'comprise, for example, a transmitted pulse 124 and one or more echo pulses I22, 523, i24 etc. Even though the-object producing the reflections is moving with respect to the observing -sta- "-tionQ-this movement produces such a slow corresponding movement of the echoes along the reference axis that each'series has its echo pulses -1n-substantially the same position a the corresponding echo pulses in the preceding and fol- "lowing series. TBetween each of the echo pulses and also contributing'to them are spurious varia tions designated bythe referencecharacter I25. These'spurious or noise variations have peaks which are not necessarily in thesame position in :each 'ser'ies. While the transmitted pulses and :the'ir-echoes'in the outputof the receiver l3 may bein either the positive or negativedirection, the :amplifier 26 serves to amplify and (if necessary) to invert the phase of theseipulses to produce the "wave shown in Fig. 5,'line A. This wave is applied to the tubeVl through the couplin condenser 21. Grid 'bias is :provided by means of the condenser' ZZ'andthe resistor 23 shunted thereacrcss, these 'two elements being connected between the cathode and ground, and a resistor-25 connected between cathode and the plus -volt supply. -A' leak resistor 24 and an anti-sing resistor 25 are also included in the circuit between ground andthe control-gridofthis tube. The-screen grid is connected .to the positive terminal 21 of the 150-volt supply, while the anode is connected "through the anode resistor28 to the-positive terminal 29 of a source of direct potentialoi about -3U0wolts. "The bias produced by the members 22, 23 and 26 is adjusted so that all portions of --the volta'ge wave shown in Fig. 5,3line A, below the dotted line I26, designated :the cut-ofibias of the tube VI, do not produce a corresponding output current. The output current of the tube VI is shown in Fig. 5 at line B. Thi output is applied to the tuned circuit comprising the condenser 30 and the inductance member 3I. The pulses I3I, I32, I33 and I34, etc, which, if desired, may have the same height (by a proper choice of circuit constants for VI and its associated circuit elements so that the voltage peaks I2I, I22, I23, I24, etc., are sufficiently high to cause saturation), shock-excite the tuned circuit comprising the elements 30 and 3I and tend to produce an oscillation such as that shown at line C in Fig. 5. The leading edges of the current pulses I3I, I32, I33 and I34 produce negative pulses I4I, I42, I43 and I44 in the input of the tube V3 but any further oscillations are damped because on the first positive pulse following each of the negative pulses I4I, I42, I43 and I44, grid current is established in tube V3 thus damping the oscillations. Negative pulses shown in Fig. 5, line C are applied directly to the control grid. of the tube V3. The cathode of this tube is connected to the suppressor grid thereof and to ground. The screen grid is connected to the positive terminal of the source of 150 volts. The anode of the tube V3 is connected through a resistor 34 and equalizing inductance member 35 to the positive terminal of the source of 300 volts. The input circuit of the amplifier 36 is connected between the anode of the tube V3 and ground. The tube V3 is driven below cut-ofi by the negative peaks of the pulse I M, I42, I 43 and I44 and grid current in this tube suppresses the positive peaks of these pulses so that in the voltage output of the tube V3 appears pulses I5I, I52, I53 and I54, shown at line D of Fig. 5, representing only the portions of the pulses in line C which lie between the cutofi potential and cathode potential of tube V3. The pulses shown at line D are all of substantially the same height and duration since the height is determined by the operating plate current in the tube V3 in the absence of a pulse and their duration is determined by the period of oscillation of the tuned circuit. Neither of these quantities is afiected by the exact size and shape of the input pulse. The amplifier 36 amplifies, and, if desired, further clips the output of the tube V3 to produce a series of pulses such as is shown in Fig. 5, line E, all of which are of the same amplitude and duration, the beginning of each pulse being substantially coincident with the beginning of the corresponding transmitted pulse or echo in the series of pulses shown in Fig. 5, line A. Depending upon the number of stages or the circuit connections in the amplifier 36, the pulses I6I, I62, I63 and IE4 are either positive or negative. By way of example, they have been shown as positive pulses in line E, Fig. 5. By varying the constants of the tuned circuit 30, 3I the duration of each of the pulses I4I,- I42, I43 and I44 can be varied, but this duration must be less" than the duration of the pulses in the output of the clipper tube VI. Varying the duration of the pulses I4I,

I32, I43 and I 44 varies the duration of each of L the output pulses IN to I64, inclusive. The output pulses from the amplifier 36 canbe applied through the coupling condenser 31 to the terminals 38 and 39 connected to the pulse utilization circuit I5. A resistor 46 can be included across 2 in place of the portion thereof between these 'lines. In the modified circuit, a diode V2 is provided and so placed in the circuit that its cathode supply through resistor 54. The screen grid of this tube is connected to the positive terminal of the source of volts, while the anode is connected through the resistor 55 and the high frequency equalizing inductance member 56 to the positive terminal of the source of 300 volts. The anode of the tube V3 is connected to the amplifier 36 through a clipping amplifier 60. p

The circuit shown in Fig. 3 operates as follows:

The voltage input to the tube VI is shown in Fig.

6, line A, and this is, of course, the same as in the circuit of Fig. 2. Moreover, the current output of the tube VI as shown in Fig. 6, line B, is the same as that shown in Fig. 5, line B. The voltage input to the tube V3, however, is quite different from the corresponding voltage input shown in Fig. 5, line C. This voltage input wave, which is shown in line C of Fig. 6, comprises a number of very small'negative pulses, I90, I9I, I92 and I93, produced at the times of the leading edges of the pulses I3I, I32, I33 and I34, but

which are quickly damped because of the fact that the diode V2 is made conducting by each negative pulse, thus preventing the formation of all succeeding oscillations; At the trailing edge This voltage is applied to a clipping amplifier 60 which may be connected in the same manner as the tube V3 in Fig. 2, to produce a series of output wave 22I, 222, 223 and 224, formed in. the

manner-that'the pulses I5I, I52, I53 and I54 are formed in the circuit of Fig. 2. These pulses are amplified by the amplifier 36 to produce pulses 23I 232, 233 and '234 like those shown in line D of Fig. 5, the only'difierence being that the beginning of each of the pulses in Fig. 6, line F, coincides substantially with the trailing edge of the various pulses shown in Fig. 5, line A, and Fig. 6, line A, instead of coinciding with the leading edge thereof as in the circuit of Fig. 2. It will be apparent that if pulses I3I, I32, I33 and I34 have different durations, the spacing between the various pulses 23I, 232, 233 and 234, will not be the same as that between the pulses I6I, I62, I63 and I64, comprising the output voltage pulses of the circuit shown in Fig. 2. v I

In the modification shown in Fig. 4, the condenser 30 has been made relatively large and functions largely as a blocking condenser and a condenser 6| has been connected in parallel with the inductance member 3|. The plate resistor 28 in Fig. 2 is assumed to be very large when using the embodiment shown in Fig. 4. The connections of the tube V3 are otherwise the same as in Fig. 2 and corresponding elements have been given the same reference characters in the two figures. When a current wave such as that shown in line B of Fig. 7 (which is exactly the same as that shown in Fig.

: hne B) "producedzfrom the voltage input shown Fig. 27, line at -(which corresponds ito that ashownliniFig. L5,.line A) :isapplied to the tuned circuitacomprising the capacity member 01 and theinductance member 3l and the condenser BI is charged toa negative potential to produce the leading portionof each of the waves 30!, 302, 303 and 304, shownin line Cof Fig. 7. The trailing portion of each of these pulses is produced by the condenser discharging through the induct- ;ance member '31, .but the oscillation is prevented from going far in the positivedirection because .of grid current :being set up .in tube V3, thus "damping the :oscillation. Fig. 7., line D, :showsthe output pulses 31-1, 3l2,'3|-3 and 3M of the tube V3 produced in a similar manneras the pulses I51, I52, I53 and I54 in the circuit 'of Fig.2. These'pulses are amplified bythe amplifier 3.6 as in the circuitofv-Figp2. In the oscillationsshown at :line 'C of Fig.7, the pulses'30l, 302, 303 and 304 intercept the-zero axis ,at a "point where the time t is very nearly given by the expression T At 4 2 rwhere If f f) T=- which is .the period of the oscillation as deter- .mined by .theconstants of the tuned circuitand At=duration of the driving pulses 13.1, [32, (13.3 .and I34. .The time t is taken equal tozero at the start of the input pulse. Thus, .if the width .At variesas in the pulses shown .inFig. .7, ,line B, the width of the pulses 321, 322, 32.3, and 324 varies slightly.

The-choice of circuit, that is, whether that of Fig. .2, or oflFig. 2 as modified bylsubsti'tuting "leading edge of the input pulse, and the latter when the output-pulses are-to be initiated'substantially simultaneously with the trailing edges of the input pulses.

While there have been shown andparticularly described certain embodiments .of the invention for the purpose of explaining .its principles and showing its application, it will be obvious to those skilled in the art that many other modifications and variations are possible and it is therefore intended to cover all such modifications and Variations as fall within the scope of .the inven tion which is defined in the appended claims.

What is claimed is:

'1. The combination o'f.means for receiving a series of pulses spaced apart in time, means for utilizing said pulses to produce a corresponding series of pulses comprising a tuned circuit including a series-connected capacity member, a "source of direct potential and .an inductance member whereby, in .theabsence .of a received {8 :pulse, :the :capacity member is charged. to subistantially the voltage of said source, means :for causing each of said received pulses to :change the potentials on both the terminals-of thenapac- 'ity member by substantially the same amount to cause thezpotential of the terminal of "the inductance member remote from said source to become negative with respect to the other terminal thereof, allowing said capacitymember "to begin to discharge'through said inductance member whereby a substantially cosinusoidal oscillation is started the period of which depends upon the constants of said capacity and said inductance member, unilaterally conducting damp' ing means connected acrosssaid inductance memher and .so poled that current ilows there'through when the terminal of said inductance member remoteirom-said source becomes positive with'reaspect to the other terminal thereof whereby said damping means damps the oscillation after-approximately one quarter of an oscillation cycle, and means for utilizing the potential changes across sa-id'damping means to produce said second series of pulses.

2. The combinationof claim 1 in which said damping .means is an electronic space discharge device having a cathode, an anode and a current .control element, said cathode being connected to the terminal -.'of said inductance ele- .ment remote from said condenser and said control element being connected to the other terminal of said inductance element.

3. The combination :of claim 11 in which said :dampingmeans is-an amplifyingspace discharge device jhavinga cathode, an anode and a current control element, said cathode being connected to the terminal of saidinductance element remote from said condenser and -said control ele- .ment being connected to the other terminal of said inductance element, said space discharge device being driven below cut-oil value when the potential 'of the terminal member of the inductance member remote from said source becomes negative with'respect'to the other terminal there- ;of, whereby substantially rectangular pulses appear in the anode-cathode circuit of said space discharge device.

BERNARD 'M. OLIVER.

REFERENCES CITED The following references are of record in the 'file of this patent:

UNITED STATES PATENTS 

